Is my SWG math correct

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Gecrabill

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Bronze Supporter
Feb 24, 2014
71
Osprey, Florida
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I have a GoldlineBlue essence 20k SWG. The output is 0.725lbs/day, it says So...
11.6 oz of chlorine gas if it were on 24 hours/day. Or ~0.48 oz/hr
I have my pump set to run 8 hours per day
The pool sits in Full Florida Southern exposure sun from 9am-5pm.
My guestimate loss is 3ppm/day
So I need to run my SWG 6.5 hours/day
So at an 8 hour pump runtime, I need to set my SWG at about 82%.
My CYA is right at 80.
Please let me know if this math is coming out right. Also, does 3ppm/day sound reasonable or typical? Should I start my pump to run before the sun comes up, to have the SWG running a little prior to the sun coming up? Or just leave the pump running on its 9-5 schedule?
 
Something is not quite right.

Running 24/7 at 100% the 11.6 oz of chlorine gas would add 7.9ppm of FC to your pool (use effects of adding chemicals at the bottom of PoolMath). Running at 8 hours, you would get 1/3 of that = 2.6ppm with it set at 100%. So an 8 hour run time may not be adequate.

Maybe the confusion is that an oz of chlorine gas does NOT equal 1 ppm of FC.

It is typical to lose 2-4ppm of FC per day. I think you might want to set the SWG at 100% for you 8 hour run time and see how the FC level behaves. If it is too high, I would lower the pump run time before lowering the SWG output because 8 hours is likely much more than you need, see Determine Pump Run Time.
 
3 ppm/day is high for a SWG. What CYA level are you using? We recommend CYA be between 70 and 80 with a SWG.

Time of day that you run the pump/SWG really doesn't matter, unless you have time of day electric rates.
 
Ok, so I would need approximately 4.5 oz of chlorine gas or ~ 10 hours run time. But it just isn't adding up. I know the SWG is trial and error. The problem I am running into is that I seem to be needing to SLAM about every 2 months or so. I am diligent about FC testing. I just replaced about 20% of my water due to high CH. All was running smooth for about a week, then I noticed the water changing a little color. Now I am on day 5 of the SLAM and want to try mathematically getting this thing right. The SWG is a T cell 5, says for 20,000 gallon pools. Jason, what is a typical FC loss with a CYA of 80. Also, it just gets beat by the sun. I mean full exposure, so much that even the pavers stay hot well past midnight.
 
You would need a little over 9 hours of 100% run time to add 3ppm ... but like Jason said, it would not be typical for the FC loss to be that high for a SWG with a CYA of 80ppm.

What FC level are you maintaining for the SLAM currently? Are you doing the SLAM with the SWG turned off?

Before the SLAM, what FC level were you maintaining?
 
I replaced the water about 2 weeks ago. Prior to replacing water, my cya was at 70 and FC at 5ppm. After I replaced the water, CYA was at 50ppm. I was maintaining the FC at 6ppm. I then added CYA to bring it up to 80ppm. This is when the trouble happened. Right now I am maintaining SLAM at 38ppm. A little on the high side, I know, but like to be safe. Since building the pool and reading the site. I have found that I need to keep my FC a little higher then recommended levels. So where the target is 6, seems like I will likely need 7 or 8 to maintain.
 

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Gecrabill said:
The SWG is a T cell 5, says for 20,000 gallon pools.
Click to expand...

Math aside, that's a fairly small cell even for an 11,000 gal pool and will probably require a lot of run time.

While dialing in my T-15 cell I tested FC daily using the FAS-DPD test to figure out where to set it to pretty much maintain my desired level of FC. From there it has only required small (10%) one way or the other.
 
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